Question

A short bar magnet is placed with its south pole facing geographic south and the distance between the null points is found to be 16 cm. When the magnet is turned pole to pole at the same place then the distance between the null points will be:

• A. same along the axial line
• B. same along the equatorial line
• C. $16\times 2^{\frac{1}{3}}$ times on the axial line
• D. $\frac{16}{2^{\frac{1}{3}}}$ times on the equatorial line

Answer 1

The correct option is D $\frac{16}{2^{\frac{1}{3}}}$ times on the equatorial line

$B_1$ for axial and $B_2$ for equatorial
$(d_1=16)$
$B_1=\frac{2{\mu }_{o}m}{4\pi d_1^3}$
$B_2=\frac{{\mu }_{o}m}{4\pi d_2^3}$
$B_1=B_2$
$d_2=\frac{16}{2^{1/3}}$